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Language, legal counselling and asylum : a linguistic ethnography of immigration law firms in Belgium
No full textHydrogeological investigation of a volcanic aquifer system on the flanks of Mount Meru, Northern Tanzania
No full textIn the Arusha volcanic region in northern Tanzania, within the eastern branch of the East African Rift System, water shortage is common and much of the surface water and groundwater contain fluoride (F⁻) concentration above the WHO limit (1.5 mg/L) recommended for drinking water. The groundwater is the main source of drinking water in the area. Prolonged intake of this high F⁻ water has caused dental and skeletal fluorosis among the local population. Limited studies particularly concerning the aquifer structure, groundwater potential, groundwater flow systems, and localities of low F⁻ groundwaters have been conducted in the area. In this study, primary data (field collected) and secondary data were used to study the aquifer characteristics, hydrochemistry, hydrogeochemistry, groundwater recharge, groundwater flow systems, and hydrothermal reservoir in the study area. The delineation of the aquifer structure and estimation of its hydraulic properties have been conducted with the aim of investigating the groundwater potential for different geological formations, to provide comprehensive knowledge for proper groundwater utilisation and management. The groundwater level monitoring was done for uncovering the spatiotemporal variation of groundwater levels in the aquifer and analysing the groundwater level response to rainfalls. Moreover, the characterisation of high F⁻ groundwater in the aquifer system has been done to understand the temporal and spatial changes in the groundwater chemistry, develop a conceptual groundwater flow model, and evaluate the hydrogeochemical processes responsible for temporal and spatial changes in the groundwater chemistry with the aim of identifying localities of low and high F⁻ groundwaters for the purpose to come up with guidelines to provide groundwater that can be used for drinking water supply without health impacts on the population. Lastly, the estimation of the temperature and circulation depth of the hydrothermal reservoir below the ash cone of Mount Meru was done to explore a possibility of finding low-temperature geothermal energy resources on the flanks of Mount Meru and develop a conceptual model for the hydrothermal reservoir in the area.
The delineation of the aquifer structure using litho-hydrostratigraphical cross-sections and estimation of the hydraulic parameters using single well pumping tests show that the aquifer system on the flanks of Mount Meru is a sloping aquifer with sloping beds. On the far east of the eastern flank, the aquifer is composed of debris avalanche deposits, while on the north-eastern and west flanks the aquifer is composed of weathered fractured lava, whereas on the south-western flank, the aquifer is composed of different layers: pyroclastics on the top, weathered fractured lava, weathered pyroclastics, and again weathered fractured lava at the bottom. The aquifer is semi-confined on the north-eastern flank, by overlying debris avalanche deposits acting as an aquitard, while unconfined elsewhere. The transmissivity of the aquifer on the north-eastern flank is substantially increasing with increasing depth, while on the south-western flank, the transmissivity of the aquifer is variable, both at the shallow depth (exploited by hand-dug wells) and at larger depth (exploited by boreholes); indicating aquifer heterogeneity. On the north-eastern flank, the topmost part of the aquifer, exploited by hand-dug wells, has a low transmissivity (T=1.3 m2/d) and potential for smaller withdrawals for local water supply with limited consumption, while the upper part of the aquifer, captured by boreholes, has an intermediate transmissivity (T=35 m2/d) and potential for local water supply, whereas the deeper part of the aquifer has a high transmissivity (T=788 m2/d) with potential of somewhat regional importance. On the western flank, the aquifer has a very low transmissivity (T= 0.4 m2/d) and potential for local water supply with limited consumption. On the south-western flank, on average, the topmost part of the aquifer, exploited by hand-dug wells, has very low to intermediate transmissivity (range of T: 0.3–19 m2/d), leading to variable potential for smaller withdrawals for local water supply (private consumption), whereas the deeper part of the aquifer, captured by boreholes, has low to intermediate transmissivity (range of T: 9–43 m2/d) and potential for local water supply.
For the analysis of the groundwater level response to rainfall in the shallow aquifer system on the flanks of Mount Meru, a conceptual model of groundwater flow has been defined, related to sloped aquifers, localised recharge, and propagation of groundwater waves (or pulses). The model has been used to explain the piezometric time series in the area. Groundwater flow on and around Mount Meru is occurring in shallow aquifers on the slopes of the mountain. Because of the large topographic differences and steepness of the slopes as well as the depositional mechanism, aquifer beds and layer bottoms show significant tilt and groundwater flow is not only controlled by piezometric gradients but also by gravity effects. The conceptual model was verified in the time series from monitored wells on all sides of the mountain and can explain the water level variations that are observed. Thus, the estimation of groundwater recharge using the water-table fluctuation (WTF) method or using models that utilise Darcy’s flow equation is unfit for the estimation of the diffuse recharge in the area. On the south-western flank of Mount Meru, the water level variations are very smooth, indicating a high hydraulic diffusivity in this aquifer. The geomorphology of the landscape in the study area plays a great role in controlling the groundwater flow paths. The general groundwater flow system on each flank is involving a multidirectional flow from the higher elevation areas, including the parasitic cones, towards the lower areas.
The characterisation of high-fluoride groundwater in the aquifer system on the flanks of Mount Meru, focusing on parts of the flanks that were only partially or not at all covered by previous research, and the analysis of the impact of rainwater recharge on groundwater chemistry by monitoring spring discharges during water sampling show that the main groundwater type in the study area is NaHCO3 alkaline groundwater (average pH = 7.8). High F⁻ values were recorded: in 175 groundwater samples, the concentrations range from 0.15 to 301 mg/L (mean: 21.89 mg/L, median: 9.67 mg/L), with 91% of the samples containing F⁻ values above the WHO health-based guideline for drinking water (1.5 mg/L), whereas 39% of the samples have Na+ concentrations above the WHO taste-based guideline of 200 mg/L. The temporal variability in F⁻ concentrations between different seasons is due to the impact of the local groundwater recharge. We recommend that a detailed ecohydrological study should be carried out for the low-fluoride springs from the high-altitude recharge areas on the eastern and northwestern flanks of Mount Meru inside Arusha National Park. These springs are extracted for drinking purposes. An ecohydrological study is required for the management of these springs and their potential enhanced exploitation to ensure the sustainability of this water extraction practice. Another strategy for obtaining safe drinking water could be to use a large-scale filtering system to remove F⁻ from the groundwater.
The investigation of the localities of low and high F⁻ groundwaters using the conceptual groundwater flow model and hydrogeochemical system analysis in the aquifer system in the study area for the purpose to come up with guidelines to provide groundwater that can be used for drinking water supply without health impacts on the population, shows that the groundwater chemistry of F⁻-rich NaHCO3 alkaline groundwater in the area is controlled by dissolution of weathering aluminosilicate minerals (especially Na-K-feldspars), dissolution of F⁻-bearing minerals, the precipitation of carbonate minerals as secondary products and the dissolution of magmatic gases. Evaporative concentration of solutes, precipitation and redissolution of evaporitic salts may locally play a role, especially on the north-eastern flank of Mount Meru. The low F⁻ groundwaters which can be used for drinking water supply without health impacts under the WHO limit (1.5 mg/L) are the low-fluoride springs from the high-altitude recharge areas on the eastern and north-western flanks of Mount Meru inside Arusha National Park, whereas on the western flank the groundwater meets the Tanzanian limit (4.0 mg/L). On the south-western flank, the shallow aquifer composed of alluvium deposits at lower elevations, shows F⁻ values that meet the Tanzanian limit. One of the three investigated deep boreholes on this flank also meets the Tanzanian limit, this suggests a possibility of finding more localities of relatively low F⁻ groundwaters in the deep aquifer. Yet, in general, the deposits at lower elevations (the debris avalanche deposits, mantling ash, alluvial fan deposits and lake deposits) are found to contain high to very high F⁻ values, whereas the deposits at high elevations (pyroclastics and lavas) contain groundwater of low F⁻ values. Thus, the internal texture and grain size of geological formations (causing variable weatherability), the burial depth of these formations (less weathering at depth) and the water residence times are the factors determining the groundwater mineralisation and F⁻ concentrations in the area. Deposits that are more weathered (e.g., debris avalanche deposits, mantling ash, alluvial fan deposits and lake deposits) have higher F⁻ values, whereas deposits at larger burial depths (e.g., fractured weathered lava) are less weathered and have low F⁻ values. Groundwater with a longer residence time (i.e., mature water) has a high F⁻ value, whereas groundwater with a shorter residence time (i.e., young water) has a low F⁻ value. The study identified that the deep hydrothermal system has influence on the high F⁻ groundwaters on the eastern and north-eastern flanks of Mount Meru.
The estimation of the temperature and circulation depth of the hydrothermal reservoir below the ash cone of Mount Meru by using classical solute geothermometry analysis of the two hydrothermal springs located at the foot of the ash cone shows that, using silica geothermometers, the estimated reservoir temperatures range from 50–90 °C (average temperature: 75 °C), indicating a low-temperature hydrothermal reservoir. We would expect higher temperature on an active volcano, such as Mount Meru, the low temperature can be attributed to a great extent of cold groundwater mixing with the hydrothermal waters. The estimated circulation depth of the hydrothermal springs ranges from 0.6–1.4 km deep; the circulation depth may be shallower, since the faster velocity along the fractures will result in shallower depth of circulation (and water-rock interaction). Therefore, there is a possibility of finding low-temperature geothermal energy resources on the eastern flank of Mount Meru since the deep hydrothermal system has influence on the groundwater chemistry on the eastern and north-eastern flanks of Mount Meru. A preliminary conceptual model for the hydrothermal reservoir in Mount Meru is presented in this thesis. We recommend further working towards proving the existence of a potential groundwater reservoir below the ash cone, as well as a detailed analysis of the hydrothermal system in the area
High-volume replacement of cement by non-ferrous-metallurgy slag and impact of limestone, fineness and grinding aids
No full textThe global need for greenhouse gas emission reductions can only be met through an
immense effort from many industries, among which the cement and concrete industry,
considering that the production of cement accounts for approximately 8 % of the total
anthropogenic CO2 emissions worldwide. One of the most promising pathways to a
reduction of these emissions is by avoidance of clinker production via (partial)
replacement of Portland cement (PC) with so-called supplementary cementitious
materials (SCMs) that react in the alkaline, Ca(OH)2 rich environment created by the
hydrated PC. Considering the high required reduction of greenhouse gas emissions,
high-volume replacement levels with such materials need to be utilized. However,
several of the currently most commonly used SCMs are coming under pressure as the
production processes where they originate as by-products are changing under
influence of the same greenhouse gas reduction trend. There is thus a need for new
sources of SCMs, which could be partially filled by the use of slags originating from
the non-ferrous metallurgical (NFM) industry, thereby contributing to another global
trend of circular economy and waste reuse and recycling. These slags are typically
rich in Fe(II), which is very distinct from most cementitious systems, which have
limited Fe content which is present almost exclusively as Fe(III). This implies a
significant potential impact on the hydration process, hydration products and
properties, which had thus far not been thoroughly investigated or understood.
In this work the replacement of PC by up to 70 wt.% of NFM slag in blended cements
is investigated. First, the hydration process of the simple binary PC – NFM slag binder
was studied. This indicated a retarding effect of the NFM slag on the early hydration
reactions of PC. From 2 days onwards, however, the reaction extent of PC was
continuously increased with increasing NFM slag content. Later on, beyond 7 days
aging, the NFM slag started reacting, reaching a reaction degree of 20-25 % after 150
days with no significant change between for differing replacement levels. This is
similar to the commercially used siliceous fly ashes, which is being phased out in
several regions, such as Europe. Through the reactions, the components released from
the NFM slag contributed to the formation of hydration products, such as increased
AFm phase formation, and increased the Si/Ca, Al/Ca and Fe/Ca molar ratios of
calcium-silicate-hydrate (C-S-H) phase. Among these hydration products a phase was
found that was not previously observed for (blended) cements, and identified as a
(Fe(II), Mg(II))-Al(III))-layered double hydroxide. This phase, along with siliceous
hydrogarnet and C-S-H were found to be the main Fe containing hydration phases in
the blended cements with up to 50 wt.% NFM slag, while siliceous hydrogarnet could
not be detected in blended cement with 70 wt.% NFM slag. The (Fe,Mg)-Al-layered
double hydroxide phase was further investigated with respect to its composition and
oxidation behavior, revealing a peculiar mechanism of in-situ oxidation, without
decomposition, up till now only observed for Fe(II)-Fe(III)-layered double
hydroxides.
Since durability of the resulting mortar or concrete is an important aspect, required
for any valorization of these slags in blended cements to be viable, it was investigated
as well. Particularly the resistance of concrete with 30 or 50 wt.% NFM slag in the
binder to carbonation, chloride ingress and freeze-thaw conditions was investigated,
complemented by a simplified study of their cost and environmental impact. When
30 wt.% of NFM slag was present, the resistance to carbonation and chloride ingress
was found to be slightly reduced or similar to the reference concrete without NFM
slag. The environmental impact was only slightly reduced due to the high CO2
emissions from the slag pre-treatment process. Yet, the development of future
treatment processes with lower CO2 impact could lead to considerable reductions in
environmental impact. The presence of 50 wt.% NFM slag on the other hand reduced
the resistance to both carbonation and chloride ingress. For both replacement levels,
the resistance to freeze-thaw conditions was poor, showing the importance of air
entrainment agents for these concretes. A simplified economic analysis indicated a
cost reduction of the concretes could be obtained by incorporating NFM slag in the
binder, depending on the mix-design and the desired properties. Hence, provided the
cost of pre-treatment and milling below such a concrete cost reduction, the use of
NFM slags may also yield cheaper concrete.
Going beyond the simple binary binder, the use of limestone and its impact on blended
cement with 50 wt. % and 70 wt. % NFM slag was then studied. While neither the
clinker or NFM slag reaction degree changed significantly, other phases were
promoted leading to more bound water by the reacted NFM slag. Therefore, any
reacted NFM slag fraction was more efficient with respect to space-filling and by
extension compressive strength. When 50 wt.% of PC was replaced by NFM slag and
limestone, an optimal compressive strength was reached for a limestone/NFM slag
weight ratio of 1/9, corresponding to 5 wt.% limestone addition.
The reactivity could be enhanced appreciably by an increase of the fineness and thus
surface area of the NFM slag from 4500 cm2
/g binder to 6500 cm2
/g binder, where PC
typically has a specific surface area of around 4000 cm2
/g. However, it also led to an
even stronger retarding effect on the early PC hydration reactions. This was
investigated in more detail but none of the theories proposed in literature for other
NFM slags or for some fly ashes showing similar effects could explain this retardation.
Nevertheless, it was found that the compressive strength after 28 days was increased
significantly as a result of the enhanced slag reactivity, particularly for blended
cement with 50 wt.% NFM slag in the binder. In fact, at that age, the compressive
strength of blended cement mortar with 50 wt.% fine NFM slag was similar to that of
blended cement mortar with only 30 wt.% of less fine slag.
Since the grinding of NFM slags is known to be energy intensive and expensive, the
efficacy of several alkanolamines as grinding aids was investigated. Slight
improvement of the grinding efficiency was observed, with little effect of the exact
type of grinding aid. Furthermore, the presence of alkanolamines enhanced the
dissolution rate and inherent reactivity of the NFM slag, particularly so for the tertiary
alkanolamines triethanolamine (TEA) and triisopropanolamine (TIPA).
Correspondingly the amount of bound water increased, and this to the greatest extent
for TIPA. Yet, the compressive strength reduced rather than increased. During the
final study it was found that this was most likely caused by increased air entrainment
by these alkanolamines. In that final study, the impact of up to 0.1 wt.% TIPA on the
hydration of blended cement with 50 wt.% replacement of PC by either NFM slag
alone or by both limestone (12.5 wt.%) and NFM slag (37.5 wt.%) was investigated
in depth. This showed that TIPA only significantly affected the reaction degree of the
NFM slag beyond 7 days while at earlier times mainly the reaction degree of the ferrite
phase of the PC was enhanced. Yet, the sulfate balance was not affected by the use of
TIPA, although the maximum improvement in cumulative heat increased. About 2
wt.% of additional CaSO4 was required to obtain the optimal heat release in isothermal
calorimetry and thus compensate for the replacement of PC (which contains CaSO4)
by the other components. Furthermore, a synergetic effect of TIPA and limestone was
found, where the reaction increase of the slag through the use of TIPA was used more
efficiently through the reaction with carbonates released from the limestone. This
way, a slight increase of compressive strength could be obtained over both binary (PC
– NFM slag) and ternary (PC – NFM slag – limestone) blended cements without
TIPA, despite a higher air content when TIPA was present.
This research showed that NFM slags can be a viable alternative SCM, albeit with the
formation of a (Fe, Mg)-Al-layered double hydroxide phase that warrants further
study. Furthermore, through the use of the additions studied in this work and the
understanding of their effects, the toolbox for optimization is expanded, thereby
aiding in the valorization of these NFM slags in blended cements
Pre-digestive and digestive microbial strategies to optimize utilization by ruminants of tropical legumes with high amounts of plant secondary metabolites
No full textRuminant production is a major engine of farm development for smallholders in the tropics. It provides a source of income, employment, food as well as better nutrition. However, in many tropical regions, ruminant production does not develop to its potential due to inadequate animal feed resources both in terms of quality and quantity, particularly in grass-based systems. The climatological conditions and annual variation result in a reduction of the nutritive value (mainly because of a lower protein content and digestibility) of grasslands at the end of the rainy season (fast lignification), while the lack of precipitation during the dry season seriously impacts crop and pasture productivity which hamper feed supply. Finally, high and volatile prices of supplements, compound feeds and raw materials hamper access of smallholder farmers to such feed resources, but also from a sustainability point of view, input-intensive ruminant production systems may be questioned. Accordingly, the introduction of alternative, locally available feed resources is stimulated. Tropical legumes deserve particular attention in this respect due to their high forage and beans yield, and protein content. However, they contain several plant secondary metabolites (PSM) with anti-nutritional properties, which impair their use as ruminant feed.
Within the frame of this Ph.D. research, three tropical legumes were targeted, i.e., Canavalia ensiformis, Mucuna pruriens and Leuceuna leucocephala. With respect to C. ensiformis and M. pruriens, studies included both the mixture of forage and beans (1:1, on DM basis) as well as the beans meal while forage meal, including leaves and twigs, of L. leucocephala was studied. The potential of pre-ingestive (ensiling) and digestive microbial strategies to optimize the utilization of these tropical legumes by ruminants was studied. For this, laboratory approaches were used, including labscale ensiling and in vitro degradability assessments, as well as an in vivo trial, targeting early life interventions.
Chapter 1 introduced some background to the Ph.D. research, both from a practical as well as from a scientific perspective. The Cuban context (agrometeorological conditions, characterization of feed systems during the rainy and dry season) was introduced as well as some nutritional characteristics of the three tropical legumes studied within the frame of this Ph.D. Furthermore, the potential of ensiling to preserve legumes and diminish their PSM content was discussed. Finally, the rumen microbial metabolism largely determines the potential inclusion of unconventional feeds in ruminants diets. The crucial role of the rumen microbes was introduced in relation to PSM breakdown as well as the potential of early-life interventions to support the development of the microbial community in the rumen and to enhance acceptance of unconventional feeds by young animals.
Chapters 2 to 4 report the experimental work. A first study, described in Chapter 2, studied ensiling as a possible pre-ingestive approach to enhance the nutritive value of beans meal from both C. ensiformis and M. pruriens, which were ensiled together with sugarcane stalks (60/40) for 30, 60 or 90 days. Before and after ensiling, the chemical composition, contents of some PSM (trypsin inhibitor, L-canavanine, total tannins, L-dopa and phytic acid), as well as, the cellulase OM degradability (CDOMD) were determined. The ensiling process largely reduced (P < 0.001) the studied PSM in all silages, but this reduction was more extensive in silages with M. pruriens as compared with silages with C. ensiformis. Ensiling affected (P < 0.05) the digestibility and energy content of the feeds as compared fresh material, but no further changes were observed after 30 days of ensiling.
Further, in Chapter 3, several batch in vitro simulations of the rumen fermentation were carried out to assess the effect of different sources of ruminal inoculum on apparent degradation of whole plant meal (forage/bean (1:1, on DM basis) meal) of C. ensiformis and M. pruriens, beans meal of C. ensiformis and M. pruriens and of forage meal of L. leucocephala. Sources of ruminal inoculum used in the in vitro simulations included fresh rumen inoculum from Belgian sheep, fresh rumen inoculum from Cuban sheep and rumen inoculum obtained after 14 days consecutive batch cultures. In some experimental set-ups in this chapter both apparent degradability of the organic matter as well as of the PSM have been studied concomitantly, while other experiments have been limited to apparent degradability of OM. In all experiments with C. ensiformis, both OM and PSM of beans as well as forage/beans meals were extensively degraded during 24 h incubation, irrespective of the inoculum source. Compared with C. ensiformis, the OM degradation of M. pruriens forage/beans meal was more affected by the ruminal inoculum source, but this seemed unrelated to the ruminal degradation kinetics of the PSM studied here (i.e. L-canavanine and trypsin inhibitor), but potentially may be related to variation in degradation of tannins, which are present at higher concentrations in the forage of this legume. Forage meal of L. leucocephala was considerably less degraded compared with the other two legumes and its degradation was highly affected by the inoculum source. This could - at least partially - be related to L-mimosine, present in L. leucocephala, which was hardly degraded in the incubations with inoculum from Belgian sheep, while a more extensive ruminal breakdown was observed under the Cuban conditions. The negative effect of L-mimosine on organic matter degradability was supported in an additional in vitro experiment with straw, inoculum from Belgian sheep and with or without pure L-mimosine. Ruminal degradation of straw was 31% lower when L-mimosine was supplemented.
As adaptation of the microbial community in the rumen seemed particularly important for L. leucocephala, the introduction of this legume may be challenging after weaning of young animals, as their microbial population in the rumen is still under development. Hence, in Chapter 4, an in vivo study with goat kids was performed to assess the effects of a pre-natal and early-life nutritional intervention on feed intake and digestibility of a post-weaning diet including L. leucocephala, as well as on immune status, the composition of the rumen bacterial community and growth of the kids from 4 to 20 weeks of age. For this, a 2 × 2 factorial design trial was performed to test either or both the supplementation of L. leucocephala in the late pregnancy diet of goat does, and supplementation of live yeast to their newborns. A stimulatory effect of the prenatal exposure on the post-weaning dry matter intake of the L. leucocephala supplemented diet was observed, resulting in a higher daily gain and final body weight at 20 weeks. Differences in the immune status were relatively small and not thought to be a driving factor of differences in animal performance. Furthermore, postnatal supplementation of live yeast favoured maturation of the rumen bacterial community (i.e., greater abundance of Bacteroidetes, in particular Prevotella, and reduced abundance of Firmicutes) and stimulated the protozoal colonization. Concomitantly, organic matter digestibility was enhanced post-weaning, suggesting effects of the early-life intervention persisted and could have affected animal performance.
Chapter 5 presented a general discussion concerning the pre- and post-ingestive microbial strategies to optimize utilization by ruminants of the three tropical legumes (C. ensiformis, M. pruriens, L. leucocephala). Furthermore, prospects were formulated for further research and validation
Value and marketability : determinants of the discount for lack of marketability
No full textThe valuation of private companies is a matter of interest for many stakeholders, including valuation professionals, auditors, courts, and tax authorities. The matter is deceptively complex, notably because there is no consensus on the nature, size, and determinants of the so-called discount for lack of marketability (DLOM).
The DLOM can be defined as an amount or percentage deducted from the value of an ownership interest to reflect the relative absence of marketability. Indeed, most valuation methods lead to value indications for a marketable interest, and it is generally accepted that investors attach a lower price to assets that are not readily marketable.
The DLOM is oftentimes oversimplified as the difference in value between an illiquid (unlisted) stock and an all-else-equal liquid (listed) security. This value gap is important but ill understood. Leading scholars have noted time and time again that fair market value calculations often boil down to taking a marketable value estimate and reducing that amount by a contrived percentage. In practice, DLOMs of 20% to 40% are routinely used for valuing private businesses.
The extant literature has proposed various DLOM estimation methods that fall into two broad categories: theoretical and empirical models. All of these models have been challenged, either because they require the input of information that cannot be objectively determined for private companies (theoretical models), or because estimates based on the comparisons between liquid and illiquid valuation subjects are by nature always imperfect and thus prone to discussion (empirical models).
Nevertheless, and in the absence of better information, the empirical models, especially, have received lots of attention and the averages presented in these studies are often used in practice without much formal reasoning or economic justification.
In order to shed more light on the determinants of the DLOM we have turned to an alternative source of information that can bring additional insights. Specifically, we have turned to court decisions that decide on private company valuations, including the DLOM to be applied. The court typically justifies its decision by referring to how the specific company is situated, and the rights and obligations attached to the valuation subject. This contextual information provides more background than the pure financial information that can be found in traditional data sources.
This method which combines elements of qualitative and quantitative analysis has allowed us to demonstrate that the company’s ownership structure, its operations, the transfer restrictions on shares, the exit possibilities for shareholders, and the level of control attached to the valuation subject have a significant impact on the DLOM
Spectral X-ray computed tomography : potential and applications in geoscience
No full textAn accurate chemical characterization of a sample is often required in different scientific applications. This is often done by using two-dimensional analytical techniques. However, a major drawback of such methods is the loss of three-dimensional information, which is often necessary for a correct characterization of an object. Therefore, methods such as X-ray computed micro-tomography (micro-CT) are becoming more popular as they enable a high-resolution three-dimensional analysis of an object. Though, X-ray tomography is not able to provide any chemical information about a sample without any prior knowledge.
There have been different approaches to obtain chemical information using X-ray computed micro-tomography. This work shows a new and emerging technique called spectral X-ray computed micro-tomography (spectral-CT). This method is based on a semiconductor detector that is able to directly detect incoming X-rays and convert them into a digital output. Therefore, it is possible to analyze the X-ray spectrum, which contains a lot of different information about the measured sample based on the interaction between X-rays and the sample itself. By using the position of absorption edges in the X-ray spectrum it is possible to identify chemical elements within the spectral range of the detector (20 -160 keV).
In this work, the TESCAN PolyDet 1 was used for all measurements. It uses a CdTe crystal as a detection crystal, which offers a lot of advantages for the detection of high-energy X-rays due to its high atomic number. Therefore it is possible to identify elements with atomic numbers above 48 (Cd).
To show different applications and the potential of spectral-CT in geoscience different samples were analyzed. Numerous reference materials of pure elements were measured to test the performance and the limitations of the method. Moreover, different artificial mixtures of reference materials were used to simulate rock samples containing multiple phases. In addition two different application examples of spectral-CT in geosciences are presented in this work. In the first one different platinum group minerals (PGM) from the Norilsk 1 deposit in Russia are analyzed using spectral-CT. Different PGM could be identified and their three-dimensional distribution was analyzed by combining spectral-CT with high-resolution X-ray micro-CT. Moreover, the results were compared with two-dimensional analytical techniques such as scanning electron microscopy. In the second example, spectral-CT was used to analyze different ore minerals from the Witwatersrand basin in South Africa. The three-dimensional distribution of gold and different U-minerals was analyzed by combining spectral-CT with high-resolution X-ray micro-CT. Moreover, the results were compared with scanning electron microscopy.
All these examples show that spectral-CT is an evolving analytical technique, which offers a lot of advantages for the three-dimensional characterization of different materials
Unlocking the ability in disability : how and when can individuals with disabilities excel as employees or entrepreneurs?
No full textBias adjustment of climate model outputs for the stochastic generation of meteorological variables and river discharge
No full textClimate-driven extremes have become more common during the past few years. Even on the small scale of Belgium, it is clear that climate change exacerbates many extremes, such as droughts or floods. Consequently, the question arises how extremes will evolve under further climate change. By coupling different models, scientists can answer this question ever more precisely and with more certainty. Yet, there is much research yet to do, as there are many subquestions currently unanswered or with only an uncertain answer. Mathematical methods help to answer the remaining questions or to refine the answers. Stochastic methods are a very useful type of mathematical methods, as allow for expressing climate and weather in function of probability. This bypasses the complexity that can be found everywhere in Earth’s weather system.
In this dissertation, two groups of stochastic methods are discussed which are applied later in the impact modelling chain. On the one hand, bias-adjusting methods allow for adjusting the biases in climate models. However, these methods are themselves affected by climate change. On the other hand, stochastic weather generators allow for extrapolating time series and thus a better extreme value inference. Both groups of methods can be of importance when studying climate impacts, but can simultaneously increase uncertainty.
Although there are currently many challenges, such as heatwaves, droughts and floods, only the latter is focused on in this PhD. River floods have been shown to be an important challenge, whether it is on the global, European or Belgian scale. For example, the floods of July 2021 illustrated how our country is currently poorly adapted to such extremes. By focusing on extreme precipitation and floods, the problems discussed in this PhD and the resulting uncertainty on climate change impact, can be situated within a tangible framework
New to the game : a system analysis of the orientation process of newly arrived migrant students in Flemish secondary education
No full textTowards data-supported urban mobility management
No full textCities have an important role in making our mobility more sustainable. This PhD investigates whether and how new data sources can support them in doing so. To make the concept of 'sustainable mobility' more specific, we developed a set of indicators that allow cities to evaluate the sustainability of their mobility system. However, such evaluation requires mobility data as an input. Innovative data sources are expected to meet this demand, as new technologies collect data that are more focused on mobility, whereas traditional data are more traffic-related. Cities report that also capacity building and governance issues are important obstacles for a more data-supported approach.
The potential of new data sources is illustrated in two use cases based on smartphone tracking data. A first application shows how this technique provides a more complete and multimodal registration of trips, improving the quality of travel behaviour studies. A second use-case focuses on the use of bicycle data, a transport mode which typically is less well covered by classical technologies. A method was developed to measure delays for cyclists, an indicator that via classical methods would require a time-intensive manual recording. Both use-cases show how new data sources not only lead to better measurement of existing indicators, but also enable the introduction of very novel indicators.Steden hebben een belangrijke rol in het verduurzamen van onze mobiliteit. Dit doctoraat onderzoekt of en hoe nieuwe databronnen hen daarbij kunnen ondersteunen. Om het begrip 'duurzame mobiliteit' te concretiseren, ontwikkelden we een set van indicatoren die steden toelaat om de duurzaamheid van hun mobiliteitssysteem te evalueren. Dergelijke evaluatie vereist echter mobiliteitsdata als input. Daartoe wordt gerekend op innovatieve soorten van data. Nieuwe inwinningstechnieken verzamelen immers gegevens die meer op mobiliteit gericht zijn, waar klassieke data eerder verkeersgerelateerd zijn. De toepassingsmogelijkheden van nieuwe data worden geïllustreerd aan de hand van twee use-cases op basis van smartphone tracking data. Een eerste toont hoe deze techniek zorgt voor een meer complete en multimodale registratie van verplaatsingen in functie van verplaatsingsonderzoek. Een tweede use-case richt zich specifiek op het gebruik van fietsdata, een vervoerswijze die door klassieke datatechnieken net onderbelicht blijft. Er werd een methode uitgewerkt om verliestijden voor fietsers te meten, een grootheid die met klassieke methodes een tijdsintensieve manuele opname zou vergen. De cases tonen hoe nieuwe databronnen dus niet enkel leiden tot een betere meting van bestaande indicatoren, maar ook de introductie van heel nieuwe indicatoren mogelijk maken